After a year of perfect service using this same exact setup, suddenly outgoing sound is extremely bad and sometimes doesn't work at all. It seems in-going sound works fine. After doing the Voip test a couple times, the "quality of service" jumps all over the place. Most of the time, the QOS is really bad. This is surprising because I have the top of the line business service from Comcast. Any help?

If you have a cable modem, you don't have a T! connection. Don't be fooled by the term "Business Connection". In most cases, a business connection just means that they give you a static IP address and possibly place you on a different subnet then residential customers. Maybe even give you a bit more bandwidth, unlocked ports so you can host servers, etc...

This does not mean you have a dedicated trunk all for you. You are still on a cable connection which is shared with everyone else on your node. If you have a weak signal at your modem, if your neighbor is a bandwidth hog, if there is an issue with an edge router local to you on Comcast's network, you can still have a poor internet connection that is not clean enough to have good sounding audio.

It could even be a problem with something locally on your own network. You show a VPN box then connects to your modem. Can you better explain your connection and your network setup? Which piece of hardware on your network prioritizes your Voip packets in relation to where Vonage is connected? What type of data traffic are you running and has there been any new services added that are utilizing more bandwidth?